In passenger cars of the type having a self-supporting bodywork, the bodywork, including the bearing structure, is typically made from a plurality of sheet metal pieces. The hollow section bearers of the bearing structure are formed by welding together at least two deep-drawn metal sheets. An example where such hollow section bearers are used as central pillars in a vehicle bodywork is disclosed in U.S. Pat. No. 2,192,075.
The central pillars of the vehicle bodywork perform an important function in the bearing structure since they provide the necessary rigidity for the passenger compartment. As a consequence, they must be able to withstand heavy loads, especially during a side impact. Due to the requirements expected of such central pillars, the cross sectional configuration of the central pillars must have a conically upward taper over its entire vertical length and must also include a door sealing flange which extends over the entire length as a bearing surface. Furthermore, the central pillars preferably include recesses for receiving door hinges, lock bolts and the like.
In accordance with conventional sheet metal fabrication techniques, it is possible to form a central pillar member having the desired conical cross section which also includes all the necessary recesses formed integrally therewith. However, the rigidity of a hollow section central pillar fabricated solely from two sheet metal halves is insufficient to provide satisfactory protection for the passengers in a side collision. Thus, such structures require extensive and costly reinforcement measures, including the use of several additional sheet metal parts, in order to provide the necessary strength and rigidity characteristics.
The steel sheets used to construct such self-supporting vehicle bodyworks are typically shaped in a deep drawing process. While the dies used for shaping the steel sheets are relatively expensive, they do provide a cost-favorable solution for mass production since they permit large production runs. However, in view of the high investment costs for tooling, the aforesaid process is very cost-intensive for smaller production runs.
A more cost-favorable solution for small production runs is known, for example, from European patent document EP 0 146 716. In this document, a vehicle bodywork construction for a passenger car is disclosed wherein the bearing structure for the bodywork comprises hollow section frame members joined by node connector elements. The hollow section frame members are formed as extruded aluminum sections and the node connector elements are formed as light metal (e.g., aluminum alloy) castings. In addition to providing a more cost-favorable solution for small production runs, the aluminum bodywork disclosed in EP 0 146 716 is both lighter in weight and is more resistant to corrosion than a sheet metal bodywork.
However, in the specific embodiment described according to this prior art, the central pillars which connect the extruded aluminum side roof frame members to the aluminum door sills comprise sheet metal components instead of aluminum components. The reason being is that it is unconventional to use extruded sections for structural components which require a variable cross section, (such as, for example, the conical central pillar in this case) since extruded sections have a constant cross section over their entire length in view of the limitations inherent to the extrusion processes.
A frame-like bearing structure for vehicles comprising multi-chamber extruded sections fitted together by narrow chamber slots is known, for example, from Japanese Patent Document JP-A-59 050 938. According to this document, a compound bearer having diverging branch-like sections is produced by separating the outer walls of the chamber slots at specified lengthwise regions such that the resulting individual hollow sections are disposed lying freely alongside each other where they are then bent relative to each other. Thus, the hollow sections are fitted together at the non-cut points, which makes it possible to eliminate costly and (for light metals) sometimes problematical weld connections or glue connections. Thus, several branching bearers are produced from a single multi-chamber extruded section. However, this branching technique is not suitable for fabrication of an extruded section door pillar of a vehicle, since in this application it is necessary to form only a single door pillar bearer (i.e., without branching) which has an upward conically tapering trend in its lengthwise direction.
British Patent Document GB-A-575 601 discloses an extruded section rod for manufacture of a superstructure of a bus wherein flanges are formed along either side of a section chamber. These flanges are cut away in the region of window openings. This document, however, does not teach or suggest how to form the extruded section with a generally conical trend.
It is known from the prior art how to form a composite frame structure having a variable cross section. For example, published WIPO document WO-A-9 014 981 discloses an extruded box section frame member for a motor vehicle body of constant cross section which is Joined by a preshaped and generally concave sheet metal piece. The sheet metal piece partially embraces the extruded box section frame member such that an enclosed cavity region is formed. The outer convex surface of the preshaped sheet metal piece forms a portion of the outer contour of the vehicle body. This document, however, does not teach or suggest how to form a frame member with a tapering cross section constructed solely from extruded light metal components.